The evolving intergalactic medium: the uncollapsed Baryon fraction in a cold dark matter universe
Abstract
A selfconsistent treatment of the thermal and ionization history of the intergalactic medium (IGM) must take into account the growth of structure in the universe, since the mean density of the IGM corresponds primarily to timevarying uncollapsed fraction of the baryonelectron component of the matter. The collapsed fraction, in turn, can have a ``feedback'' effect on this uncollapsed fraction by releasing ionizing radiation and thermal energy and by contributing to the opacity of the universe. We have calculated the time varying density of the IGM by coupling our detailed, numerical calculations of the thermal and ionization balance and radiative transfer in a uniform IGM of H and He, including the mean effect of an evolving distribution of gas clumps embedded in a smoothly distributed ambient gas, to the linearized equations for the growth of density fluctuations in both the gaseous and dark components in a Cold Dark Matter (CDM) universe, identifying the IGM density with the uncollapsed baryon fraction.
We find that, even if the IGM is never reheated, a significant fraction of the baryons remain uncollapsed at redshifts z~4. If, instead, the collapsed fraction releases enough ionizing radiation or thermal energy to reionize the IGM by z>~4 as required by the GunnPeterson (GP) constraint, the uncollapsed fraction at z~4 is even higher. The known quasar distribution is insufficient to supply the ionzing radiation necessary to satisfy the GP constraint in the case, and, if stars are responsible, instead, a substantial metallicity must have been produced by z~4. The alternative of energy release by supernovae leads to a similar conclusion.
 Publication:

After the first three minutes
 Pub Date:
 April 1991
 DOI:
 10.1063/1.40392
 Bibcode:
 1991AIPC..222..347S
 Keywords:

 Baryons;
 Cosmology;
 Dark Matter;
 Galactic Evolution;
 Intergalactic Media;
 Universe;
 Gas Pressure;
 Interstellar Gas;
 Power Spectra;
 Radiative Transfer;
 Astrophysics;
 98.60.Hj;
 98.80.Cq;
 Particletheory and fieldtheory models of the early Universe